Electrophotographic photoreceptor

ABSTRACT

An electrophotographic photoreceptor is described comprising an N-arylamino substituted hydrazone compound represented by formula (I), (II), or (III), in a light-sensitive layer thereof provided on a conductive support; formulae (I), (II), and (III) are as follows: ##STR1## wherein X represents O, S or N--R 6  ; R 1  and R 2  each represents a non-substituted or a substituted straight or branched chain alkyl group containing from 1 to 12 carbon atoms, a non-substituted or a substituted straight or branched chain aralkyl group containing from 7 to 20 carbon atoms, or a non-substituted or a substituted aryl group, the aryl group including monovalent residues of monocyclic aromatic rings and condensed polycyclic aromatic rings having from 2 to 4 rings therein; R 3 , R 4 , R 5 , and R 7  each represents hydrogen, a non-substituted or a substituted straight or branched chain alkyl group containing from 1 to 12 carbon atoms, a non-substituted or a substituted straight or branched chain aralkyl group containing from 7 to 20 carbon atoms, a straight or a branched chain alkoxy group containing from 1 to 4 carbon atoms, an aryloxy group containing from 6 to 10 carbon atoms, an acyl group containing from 2 to 8 carbon atoms, an alkoxycarbonyl group containing from 2 to 5 carbon atoms, a halogen atom, a nitro group, a monoalkylamino group whose alkyl moiety contains from 1 to 4 carbon atoms, a dialkylamino group whose alkyl moiety contains from 1 to 4 carbon atoms, or an amido group containing from 2 to 8 carbon atoms; and R 6  represents a non-substituted or a substituted straight or branched chain alkyl group containing from 1 to 12 carbon atoms, or a non-substituted or a substituted straight or branched chain aralkyl group containing from 1 to 12 carbon atoms.

FIELD OF THE INVENTION

This invention relates to an electrophotographic photoreceptor, and,more particularly, to an electrophotographic photoreceptor whichcontains a hydrazone compound in a light-sensitive layer formed on aconductive support.

BACKGROUND OF THE INVENTION

Materials which have been employed as the photoconductive materials ofphotoreceptors used in electrophotography include inorganic substancessuch as selenium, cadmium sulfide, zinc oxide, and the like.

The process of xerography, as disclosed by Carlson in U.S. Pat. No.2,297,691, utilizes a photoconductive material comprising a supportcoated with a substance which can change its electric resistancedepending upon the quantity of exposure which it receives duringimagewise irradiation exposure, and which acts as an insulator underdark. In such a process, the photoconductive material is placed in thedark for an appropriate period of time for the purpose of darkadaptation, and then a uniform potential is created on its surface inthe dark by a source of charge. Next, it is exposed to some form ofirradiation having a pattern which possesses such an effect that thesurface charge may be diminished, depending upon relative energy borneby each part of the pattern. The thus remaining surface charge orelectrostatic latent image on the surface of the light-sensitive layeris converted into visible image by contact with an appropriate chargedetecting and developing substance. Such a developing substance,referred to as a "toner", whether it is contained in an insulatingliquid or in dry carrier, can adhere to the surface of thelight-sensitive layer according to the electric charge pattern existingthere. The toner attached to the electric charge pattern can be fixedthereon using known means, such as heat and/or pressure, or solventvapors. On the other hand, it can be transferred onto a second support(e.g., paper, film, etc.). Similarly, it is possible to transfer theelectrostatic latent image onto a second support and to develop it onthe second support.

The process of xerography, wherein image is formed in such a manner asdescribed above, is one basic type of imaging process. Fundamentalcharacteristics required for photoreceptors in the electrophotography ofthis kind are as follows:

(1) The photoreceptor can be charged to create an appropriate value ofpotential in the dark.

(2) Leakage of charges created on the surface of a photoreceptor occursin the dark only to a small extent.

(3) Selective discharging of the created charges takes place rapidlyupon exposure to a pattern of light.

Conventionally used inorganic substances as described above have manyadvantages and at the same time, have various disadvantages. Forinstance, although selenium, which has so far been prevailingly used asa photoconductor, fully satisfies the above-described requirements (1)to (3), selenium photoreceptors suffer the disadvantages that (1)conditions for the production thereof are difficult to control, andtherefore the production costs are high, (2) it lacks flexibility, andthus to shape it in a belt-form is difficult, and (3) it must be handledwith great care because it is very sensitive to heat and mechanicalimpact. Cadmium sulfide and zinc oxide are each used for the productionof photoreceptor in the form of dispersion in a resin binder. However,photoreceptors of this type do not well withstand repeated uses, due tomechanical deficiencies in smoothness, hardness, tensile strength,abrasion-resisting properties, and so forth.

In recent years, electrophotographic photoreceptors utilizing variousorganic substances have been proposed with the intention of overcomingthe aforementioned defects inherent in the inorganic substances. Atpresent some of these photoreceptors are put to practical use. Forexample, there is a photoreceptor comprising poly-N-vinylcarbazole and2,4,7-trinitrofluorene-9-one (U.S. Pat. No. 3,484,237), a photoreceptorin which poly-N-vinylcarbazole is sensitized with a pyrylium salt seriesdye (published examined Japanese Patent Application No. 25658/73), aphotoreceptor containing an organic pigment as a main component(Japanese Patent Application (OPI) No. 37543/72 (the term "OPI" as usedherein refers to a "published unexamined Japanese patent application")),a photoreceptor containing an eutectic complex of a dye and a resin as amain component (Japanese Patent Application (OPI) No. 10735/72) and soon. These photoreceptors have excellent characteristics and seem to beworthy of practical uses. However, taking into account variousrequirements for photoreceptors useful for electrophotography, fullysatisfactory photoreceptors have not yet been obtained. Although theproperties required for an excellent photoreceptor depend to some extentupon the end use thereof and the method employed for the productionthereof, the use of an excellent photoconductive substance is generallythe key to the production of photoreceptors possessing excellentcharacteristics.

Photoreceptors which utilize hydrazone compounds as photoconductivesubstances are described, for example, in U.S. Pat. No. 3,717,462, whichcorresponds to published examined Japanese Patent Application No.8137/73, Japanese Patent Application (OPI) No. 59143/79, whichcorresponds to U.S. Pat. No. 4,150,987, Japanese Patent Application(OPI) Nos. 52063/80, 52064/80, and so on. In each of these cases,condensed polycyclic compounds or N-alkylamino substituted compounds ofhydrazone are employed. However, these compounds have insufficientstabilities to oxidation with ozone generated by corona charging, lightand heat, and unsatisfactory dark decay characteristics, and so on.

The hydrazone compounds having carbazole rings as described in JapanesePatent Application (OPI) No. 46760/80 are improved in their stabilityand dark decay characteristics to a considerable extent. However, theimprovements in the stability and the dark decay characteristics arestill insufficient, and, furthermore, these carbazole compounds suffer aserious disadvantage in that it is hard to obtain pure compounds becauseof difficulties in synthesizing them, and therefore production costs arevery high.

SUMMARY OF THE INVENTION

Bearing in mind the foregoing, it is an object of this invention toprovide electrophotographic photoreceptors which utilize photoconductivesubstances exhibiting further improved properties.

We have now found that particular hydrazone compounds having theformulae (I) to (III) illustrated hereinafter function efficiently as aphotoconductive substance for the electrophotographic photoreceptor andexhibit excellent properties as a charge carrier transport substance.

In accordance with this invention, it has been found that the use ofN-arylamino substituted hydrazone compounds as a photoconductivesubstance in the electrophotographic photoreceptor improves (1)stability to oxidation due to ozone generated by corona charging, lightand heat, and (2) dark decay characteristics, and further, raisessensitivity, reduces residual potential which causes fog, reducesvariations of residual potential and sensitivity which result fromrepeated uses, and confers excellent durability upon the photoreceptor.In addition, the hydrazone compounds of this invention can be relativelyeasily obtained in a pure state, and therefore can be produced at a lowprice.

More specifically, the above-described object of this invention isattained with an electrophotographic photoreceptor which has alight-sensitive layer containing a hydrazone compound represented byformula (I), (II) or (III): ##STR2## wherein X represents O, S or >N--R⁶; R¹ and R² each represents a non-substituted or a substituted straightor branched chain alkyl group containing from 1 to 12 carbon atoms, anon-substituted or a substituted straight or branched chain aralkylgroup containing from 7 to 20 carbon atoms, or a non-substituted or asubstituted aryl group, the aryl group including monovalent residues ofmonocyclic aromatic rings and those of condensed polycyclic aromaticrings having from 2 to 4 rings (wherein R¹ and R² may be the same as ordifferent from each other); R³, R⁴, R⁵ and R⁷ each represents hydrogen,a non-substituted or a substituted straight or branched chain alkylgroup containing from 1 to 12 carbon atoms, a non-substituted or asubstituted straight or branched chain aralkyl group containing from 7to 20 carbon atoms, a straight or a branched chain alkoxy groupcontaining from 1 to 4 carbon atoms, an aryloxy group containing from 6to 10 carbon atoms, an acyl group containing from 2 to 8 carbon atoms,an alkoxycarbonyl group containing from 2 to 5 carbon atoms, a halogenatom, a nitro group, a monoalkylamino group substituted with an alkylgroup containing from 1 to 4 carbon atoms, a dialkylamino groupsubstituted with alkyl groups containing from 1 to 4 carbon atoms, or anamido group containing from 2 to 8 carbon atoms; and R⁶ represents anon-substituted or a substituted straight or branched chain alkyl groupcontaining from 1 to 12 carbon atoms, or a non-substituted or asubstituted straight or branched chain aralkyl group containing from 1to 12 carbon atoms.

In the case wherein R¹, R², R³, R⁴, R⁵, R⁶, or R⁷ has a substituentgroup, the substituent group is preferably a halogen atom, an alkoxygroup, an aryloxy group, a dialkylamino group or an alkylthio group. Inthe case wherein R¹ or R² represents an aryl group, the substituentgroup further may be an alkyl group in addition to the above-describedgroups.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are schematic cross-sections of electrophotographicphotoreceptors of this invention.

FIG. 5 is a graph illustrating the stabilities to light of N-arylaminosubstituted compounds of this invention and those of N-alkylaminosubstituted compounds for comparison.

FIG. 6 is a graphical representation of the dark decay of surfacepotential created by charging the surfaces of photoreceptors utilizingN-arylamino substituted compounds of this invention and an N-alkylaminosubstituted compound for comparison, respectively.

DETAILED DESCRIPTION OF THE INVENTION

In the formulae (I), (II) and (III), X represents O, S or >N--R⁶ ; R¹and R² each represents a non-substituted or a substituted straight orbranched chain alkyl group containing from 1 to 12 carbon atoms, anon-substituted or a substituted straight or branched chain aralkylgroup containing from 7 to 20 carbon atoms, or a non-substituted or asubstituted aryl group, the aryl group including monovalent residues ofmonocyclic aromatic rings and those of condensed polycyclic aromaticrings having from 2 to 4 rings (wherein R¹ and R² may be the same as ordifferent from each other); R³, R⁴, R⁵ and R⁷ each represents hydrogen,a non-substituted or a substituted straight or branched chain alkylgroup containing from 1 to 12 carbon atoms, a non-substituted or asubstituted straight or branched chain aralkyl group containing from 7to 20 carbon atoms, a straight or a branched chain alkoxy groupcontaining from 1 to 4 carbon atoms, an aryloxy group containing from 6to 10 carbon atoms, an acyl group containing from 2 to 8 carbon atoms,an alkoxycarbonyl group containing from 2 to 5 carbon atoms, a halogenatom, a nitro group, a monoalkylamino group substituted with an alkylgroup containing from 1 to 4 carbon atoms, a dialkylamino groupsubstituted with alkyl groups containing from 1 to 4 carbon atoms, or anamido group containing from 2 to 8 carbon atoms; and R⁶ represents anon-substituted or a substituted straight or branched chain alkyl groupcontaining from 1 to 12 carbon atoms, or a non-substituted or asubstituted straight or branched chain aralkyl group containing from 1to 12 carbon atoms.

In the case wherein R¹, R², R³, R⁴, R⁵, R⁶, or R⁷ has a substituentgroup, the substituent group is preferably a halogen atom, an alkoxygroup, an aryloxy group, a dialkylamino group or an alkylthio group. Inthe case wherein R¹ or R² represents an aryl group, the substituentgroup further may be an alkyl group in addition to the above-describedgroups.

In the case wherein R¹ or R² is non-substituted alkyl groups, specificexamples thereof include the methyl group, ethyl group, propyl group,butyl group, pentyl group, hexyl group, octyl group, nonyl group,dodecyl group, isopropyl group, isobutyl group, isopentyl group,4-methylpentyl group, sec-butyl group and tert-butyl group. When R¹ orR² is an alkyl group having a substituent group, specific examples ofthe substituent group include chlorine, bromine, or fluorine as ahalogen atom; a methoxy group, ethoxy group, propoxy group, butoxygroup, or pentyloxy group as an alkoxy group; a phenoxy group,o-tolyloxy group, m-tolyloxy group, p-tolyloxy group, 1-naphthyloxygroup, or 2-naphthyloxy group as an aryloxy group; a dimethylaminogroup, diethylamino group, dipropylamino group, N-methyl-N-ethylaminogroup, N-ethyl-N-propylamino group, or N-methyl-N-propylamino group as adialkylamino group; and a methylthio group, ethylthio group, andpropylthio group as an alkylthio group. The alkyl groups wherein atleast any one of these substituent groups is attached to at least onecarbon atom composing the alkyl group in an arbitrary position of itschain moiety include examples of the aforementioned alkyl groups for R¹or R².

In the case wherein R¹ or R² is a non-substituted aralkyl group,specific examples thereof include a benzyl group, phenethyl group,1-naphthylmethyl group, 2-naphthylmethyl group, 1-anthrylmethyl groupand benzhydryl group. Examples of such substituent groups for thearalkyl group include the same groups as described in the case of theaforementioned alkyl groups for R¹ and R². As examples of the aralkylgroup having a substituent group, mention may be made of theabove-described aralkyl groups which each has in an arbitrary positionof its nucleus or chain moiety at least one carbon atom to which atleast any one of these substituent groups is attached.

When R¹ or R² is a non-substituted aryl group, specific examples thereofinclude a phenyl group, 1-naphthyl group, 2-naphthyl group, anthrylgroup, pyrenyl group, acenaphthenyl group and fluorenyl group. When R¹or R² is an aryl group having a substituent group, specific examples ofthe substituent group include alkyl groups, such as a methyl group,ethyl group, propyl group, butyl group, pentyl group, isopropyl group,isobutyl group, and isopentyl group, in addition to the substituentgroups described as specific examples in the case of the aforementionedalkyl groups. The aryl groups wherein at least any one of thesesubstituent groups is attached to at least one carbon atom composing thearyl groups in an arbitrary position of its chain moiety includeexamples of the aforementioned aryl groups for R¹ or R².

Preferable combinations of two groups representing R¹ and R²,respectively, include the cases wherein one is phenyl group and theother is methyl group, ethyl group, benzyl group, or phenyl group.

In the case wherein R³, R⁴, R⁵, or R⁷ is a non-substituted alkyl groupor a non-substituted aralkyl group, specific examples thereof includethe same groups described as specific examples in the case of theaforementioned non-substituted alkyl or aralkyl groups represented by R¹or R², respectively. When R³, R⁴, R⁵, or R⁷ is an alkyl or an aralkylgroup having substituent group(s), specific examples of the substituentgroup include the same groups described above for R¹ and R². The alkylgroups or aralkyl groups wherein at least any one of these substituentgroups is attached to at least one carbon atom of the alkyl groups oraralkyl groups include the aforementioned alkyl groups or aralkyl groupsfor R³, R⁴, R⁵, or R⁷.

When R³, R⁴, R⁵, or R⁷ represents a straight or a branched chain alkoxygroup containing from 1 to 4 carbon atoms, specific examples thereofinclude methoxy group, ethoxy group, propoxy group, butoxy group,isopropoxy group and sec-butoxy group. When R³, R⁴, R⁵, or R⁷ representsan aryloxy group, specific examples thereof include phenoxy group,o-tolyloxy group, m-tolyloxy group and p-tolyloxy group. when R³, R⁴,R⁵, or R⁷ represents an acyl group, specific examples thereof include anacetyl group, propionyl group, benzoyl group, o-toluoyl group, m-toluoylgroup and p-toluoyl group. when R³, R⁴, R⁵, or R⁷ represents analkoxycarbonyl group containing from 2 to 5 carbon atoms, specificexamples thereof include a methoxycarbonyl group, ethoxycarbonyl group,propoxycarbonyl group, and butoxycarbonyl group. When R³, R⁴, R⁵, or R⁷represents a halogen atom, specific examples thereof include a chlorineatom, bromine atom, and fluorine atom. When R³, R⁴, R⁵, or R⁷ representsa monoalkylamino group whose alkyl moiety contains from 1 to 4 carbonatoms, specific examples thereof include a methylamino group, ethylaminogroup and butylamino group. When R³, R⁴, R⁵, or R⁷ represents adialkylamino group whose alkyl moieties each contain from 1 to 4 carbonatoms, specific examples thereof include a dimethylamino group,diethylamino group, dipropylamino group, dibutylamino group, andN-methyl-N-ethylamino group. When R³, R⁴, R⁵, or R⁷ represents an amidogroup, specific examples thereof include acetamido group andpropionamido group.

Preferable groups represented by R³, R⁴, R⁵, or R⁷ are hydrogen, amethyl group, and a methoxy group.

Specific examples of R⁶ include the same non-substituted alkyl groups,substituted alkyl groups, non-substituted aralkyl groups and substitutedaralkyl groups as those described for R¹. Preferable examples of R⁶ area methyl group and an ethyl group.

Specific examples of hydrazone compounds represented by formulae (I) to(III) are illustrated below: ##STR3##

The hydrazone compounds represented by formulae (I), (II), and (III),respectively, can be easily produced by known methods. Particularly,each of these compounds can be prepared from a hydrazine represented bythe following formula (IV), or the mineral acid salt thereof, and anarylaldehyde represented by the formula (V), (VI), or (VII) by addingthereto a small amount of acid (such as glacial acetic acid or aninorganic acid) as a condensing agent, if necessary, and by allowingthem to undergo the condensation reaction in a solvent in a conventionalmanner. As the solvent, alcohols such as methanol, ethanol, and thelike, tetrahydrofuran, acetic acid, etc., can be used, independently orin the form of mixture thereof. ##STR4## In the formulae (IV) through(VII), X represents --O--, --S-- or NR⁶, and R¹ through R⁷ have the samemeanings as R¹ through R⁷ in the formulae (I), (II), and (III).

Each of the aldehyde compounds represented by the above-describedgeneral formulae (V), (VI) and (VII) can be easily obtained according tothe known Vilsmeier's method (described in Ber., Vol. 60, p. 119(1927)), in which an aromatic amine compound and a heterocyclic compoundare added to the Vilsmeier's reagent (which is prepared from phosphorusoxychloride and N,N-dimethylformamide) at a low temperature, and thethus obtained reaction product is subjected to hydrolysis to obtain theintended compound.

SYNTHESIS EXAMPLE Synthesis of Compound (1)

A Vilsmeier's reagent was prepared by adding dropwise phosphoryltrichloride (POCl₃) (46 g) to N,N-dimethylformamide (22 g) with stirringin an ice bath. Thereto there was added a solution (200 ml) ofN,N,N-triphenylamine (50 g) in N,N-dimethylformamide while continuingcooling in the ice bath. The stirring was continued for about one hour,and then the bath temperature was raised to about 90° C. Whilemaintaining that temperature, the stirring was continued further for twohours. At the conclusion of the reaction the reaction system was cooledto room temperature, and then the reaction product was poured into icewater. The thus obtained aqueous solution was neutralized with an alkalito separate out a yellow precipitate. The precipitate was filtered off,dried and then recrystallized from ethyl alcohol. Thus,p-(N,N-diphenylamino)benzaldehyde (43 g) was obtained.

The above-described aldehyde (3.35 g) and N-methyl-N-phenylhydrazine(1.5 g) were dissolved in ethanol (50 ml), refluxed for about one hour,and then cooled by allowing it to stand at room temperature. Thereupon,a yellow precipitate was separated out. The precipitate was filteredoff, dried and recrystallized from ethanol and a small amount ofbenzene. Thus, p-(N,N-diphenylamino)benzaldehydeN'-methyl-N'-phenylhydrazone (Compound (1)) (3.3 g) was obtained. m.p.144.5°-146.5° C.

Other compounds were prepared from corresponding hydrazines andaldehydes in the same manner as described above. Compound examples andtheir melting points are set forth below:

    ______________________________________                                                               Melting Point                                          ______________________________________                                        Compound (3)                                                                   ##STR5##                176-177° C.                                   Compound (4)                                                                   ##STR6##                 97-98.5° C.                                  Compound (5)                                                                   ##STR7##                158-159.5° C.                                 Compound (6)                                                                   ##STR8##                160-162° C.                                   Compound (18)                                                                  ##STR9##                139-141° C.                                   ______________________________________                                    

The photoreceptors of this invention contain the hydrazone compoundssuch as those illustrated above. Each of these hydrazone compounds canbe employed in any of the embodiments as are illustrated in FIGS. 1 to4.

A photoreceptor as shown in FIG. 1 is constructed of a conductivesupport 1 and a light-sensitive layer 21 provided thereon, which layer21 comprises a hydrazone compound of this invention, a sensitizing dye,and a binder (resin).

A photoreceptor as shown in FIG. 2 is constructed of a conductivesupport 1 and a light-sensitive layer 22 provided thereon, in whichlayer 22 a charge generating substance 3 is dispersed in a chargetransport medium 4 comprising the hydrazone compound of this inventionand a binder.

A photoreceptor as shown in FIG. 3 is constructed of a conductivesupport 1, a charge generating layer 5 containing a charge generatingsubstance 3 as a main component, and a charge transport layer 4containing the hydrazone compound of this invention, arranged in thatorder. Therein, the layer 5 and the layer 4 together constitute alight-sensitive layer 23.

A photoreceptor as shown in FIG. 4 is constructed of a conductivesupport 1, a charge transport layer 4 containing the hydrazone compoundof this invention and a charge generating layer 5 containing a chargegenerating substance 3 as a main component, arranged in that order.Therein, the layer 4 and the layer 5 constitute a light-sensitive layer24.

In the photoreceptor of FIG. 1, the hydrazone compound functions as aphotoconductive substance, and generation and transport of chargecarrier indispensable for photo-induced discharge are carried outthrough the hydrazone compound. However, the hydrazone compound littleabsorbs light in the visible region and therefore it is necessary tosensitize the hydrazone compound by adding a sensitizing dye which canabsorb light in the visible region to the light-sensitive layer for thepurpose of formation of image using visible rays.

In the case of the photoreceptor of FIG. 2, the hydrazone compoundconstitutes a charge transport medium together with a binder (or with abinder and a plasticizer) and, on the other hand, charge is generated bya charge generating substance, such as inorganic or organic pigment. Inthis instance the charge transport medium should possess such abilitiesas to accept charge generated mainly by the charge generating substanceand to transport the charge. To this case is attached one basiccondition, viz., that the absorption spectrum of the charge generatingsubstance must not have, particularly in the visible region, any overlapwith that of the hydrazone compound. This is because the efficientgeneration of charge by the charge generating substance necessitates thetransmission of light by the medium and the arrival of light at thesurface of the charge generating substance. The hydrazone compounds ofthis invention scarcely absorb light in the visible region, andtherefore they exhibit their effectiveness as a charge transportsubstance when used in combination with charge generating substanceswhich can generally absorb visible rays and generate charges.

In the photoreceptor of FIG. 3, light transmitted by the chargetransport layer 4 reaches to the charge generating layer 5 and in thearea at which transmitted light arrives, generation of charge takesplace. The generated charge is injected into the charge transport layer.The charge transport layer accepts the injected charge and transportsit. The apparent mechanism is that the generation of charge essential tothe photo-induced discharge is conducted in the charge generatingsubstance, and the function of charge transport is carried out by thecharge transport medium (principally by the hydrazone compound of thisinvention), and is similar to the mechanism in the photoreceptor shownin FIG. 2. In this case (i.e., FIG. 3) also, the hydrazone compoundexhibits a function as a charge transport substance.

In the photoreceptor of FIG. 4, the generation of charge takes place inthe charge generating layer 5 upon exposure to light, and the chargetransport layer 4 receives injection of the charge and transports it.The mechanism of the generation and the transport of charge, which areessential to the photo-induced discharge, is similar to those in thephotoreceptors shown in FIGS. 2 and 3. In this case also, the hydrazonecompound functions as a charge transport substance.

A photoreceptor according to FIG. 1 can be produced as follows: Thehydrazone compound is dissolved in a solution of a binder, and asensitizing dye is optionally added thereto. The resulting solution iscoated on a conductive support 1 and dried.

A photoreceptor according to FIG. 2 can be obtained by dispersing finegrains of a charge generating substance in a solution of the hydrazonecompound and a binder in a solvent, coating the resulting dispersion ona conductive support, and then drying it.

A photoreceptor according to FIG. 3 can be obtained by a method whichincludes the steps of: coating a charge generating substance by a vacuumevaporation process onto a conductive support, or coating a dispersion(which is prepared by dispersing fine grains of a charge generatingsubstance into a solvent in which a binder is optionally dissolved) on aconductive support and drying the coat; finishing the surface of thevacuum evaporation coated layer or the dispersion coated layer using atechnique such as buff rubbing; adjusting the layer thickness to aproper value, if necessary; and coating thereon a solution containingboth the hydrazone compound and a binder and drying it. The coatingsteps can be carried out by usual means, such as doctor blade, wire bar,or so forth.

A photoreceptor according to FIG. 4 can be obtained by coating asolution containing the hydrazone compound and a binder on a conductivesupport using a known means, drying the coating, and then providing acharge generating layer in the same manner as in the photoreceptor ofFIG. 3.

The thickness of the light-sensitive layer in FIGS. 1 and 2 each rangesfrom 3 to 50 μm, and preferably from 5 to 20 μm. In each of FIGS. 3 and4, the thickness of the charge generating layer is less than 5 μm, andpreferably less than 2 μm, and the thickness of the charge transportlayer ranges from 3 to 50 μm, and preferably from 5 to 20 μm.

In the photoreceptor of FIG. 1, the amount of the hydrazone compound inthe light-sensitive layer ranges from 30 to 70% by weight, andpreferably about 50% by weight, based on the total weight of thelight-sensitive layer. On the other hand, the amount of sensitizing dyeadded to the sensitive layer in order to confer sensitivity in thevisible region ranges from 0.1 to 5% by weight, and preferably from 0.5to 3% by weight, based on the total weight of the light-sensitive layer.

In the photoreceptor of FIG. 2, the amount of the hydrazone compound inthe light-sensitive layer ranges from 10 to 95 wt%, and preferably from30 to 90 wt%, and the amount of a charge generating substance is notmore than 50 wt%, and preferably 20 wt% or less.

The amount of hydrazone compound contained in the charge transport layerin the photoreceptor of FIG. 3 or 4 is, by analogy with in thelight-sensitive layer of the photoreceptor shown in FIG. 2, from 10 to95 wt%, and preferably from 30 to 90 wt%.

Plasticizers can be employed together with a binder in producing any ofthe photoreceptors shown in FIGS. 1 to 4.

In the photoreceptors of this invention, a plate or a foil of a metal(such as aluminum), a plastic film onto which a conductive metal (e.g.,aluminum) is vacuum evaporated, paper which has received a conductivityproviding treatment, or so on, can be used as a conductive support. As abinder, not only condensed resins such as polyamide, polyurethane,polyester, epoxy resin, polyketone, polycarbonate, etc., and vinylpolymers such a polyvinyl ketone, polystyrene, poly-N-vinylcarbazole,polyacrylamide, etc., but also all resins possessing both insulting andadhesive properties can be used.

As a plasticizer, halogenated paraffins, polychlorobiphenyl,dimethylnaphthalene, dibutyl phthalate, and so on can be employed.

Examples of a sensitizing dye that can be employed in the photoreceptorof FIG. 1 include triarylmethane dyes such as Brilliant Green, VictoriaBlue B, Methyl Violet, Crystal Violet, Acid Violet 6B, etc.; xanthenedyes such as Rhodamine B, Rhodamine 6G, Rhodamine G Extra, Eosine S,Erythrosine, Rose Bengale, Fluoresceine, etc.; thiazine dyes such asMethylene Blue; cyanine dyes such as cyanine; pyrylium dyes such asthiapyrylium perchlorate, a benzopyrylium salt (as described inpublished examined Japanese Patent Application No. 25658/73, etc.); andso on.

Examples of a charge generating substance employable in thephotoreceptors shown in FIGS. 2 to 4 include inorganic pigments such asselenium, Se-Te, CdS, CdS-Se and the like; and organic pigments such asazo series dyes (e.g., CI Pigment Blue 25 (CI21180), CI Pigment Red 41(CI21200), CI Acid Red 52 (CI45100), CI Basic Red 3 (CI45210), etc.),phthalocyanine series dyes (CI Pigment Blue 16 (CI74100), etc.), indigoseries dyes (e.g., CI Vat Brown 5 (CI73410), CI Vat Dye (CI73030),etc.), perylene series dyes (e.g., Algol Scarlet B (produced by BayerCo.), Indanthrene Scarlet R (produced by Bayer Co.), etc.) and so on.

In addition, amorphous silicon as described in Japanese PatentApplication (OPI) Nos. 86341/79, 116930/79, 145537/79 and so on can bealso employed as the charge generating substance.

Furthermore, in the photoreceptor produced in the above-describedmanner, an adhesion layer or a barrier layer may be optionally providedbetween the conductive support and the light-sensitive layer. Materialsemployed for such layers include polyamide, nitrocellulose, aluminumoxide and so on, and a preferable thickness thereof is 1 μm or less.

A process for carrying out copying using the photoreceptor of thisinvention includes the steps of charging the surface of thephotoreceptor, exposing the charged surface to a pattern of light,developing latent image thus formed, and optionally transferring thedeveloped image onto plain paper or the like.

The photoreceptors of this invention have advantages in that theirstability to light and heat are significantly improved and dark decay isreduced to a great extent.

In order to investigate stability to light, the hydrazone compounds(Compound (1) and Compound (3)) and N-alkylamino substituted hydrazonecompounds (represented by the following structural formulae (a) and(b)), employed for comparison, respectively, were dissolved indichloromethane solutions in the same concentration of 10⁻⁴ mol/l:##STR10##

Next, each of the solutions was irradiated with ultraviolet rays, andthe absorption spectrum of the irradiated solution was measured atregular time intervals.

The results are shown in FIG. 5. Therein, the numbers on the ordinateindicate the ratio of absorbance at the wavelength where the compound tobe investigated exhibits its absorption maximum (which is 374 nm in thecases of the hydrazone compounds of this invention (1) and (3), and 359nm in the cases of N-alkylamino substituted compounds (a) and (b)employed for comparison) before irradiation with ultraviolet rays, whichabsorbance is represented by Abs_(o), to absorbance at the samewavelength after t minutes' irradiation, which absorbance is representedby Abs_(t), calculated in terms of percentages, that is (Abs_(t)/Abs_(o))×100; that is, the degree of reduction in the absorbance at thewavelength exhibiting the absorption maximum is plotted as the ordinate,and irradiation time is plotted as the abscissa.

It is apparent from FIG. 5 that when the N-arylamino substitutedcompounds are used in place of the N-alkylamino substituted compoundsthe stability to light is significantly improved.

In accordance with embodiments of this invention, photoreceptors areobtained which have very high sensitivity, reduced residual potential(if the residual potential is high, fog will be caused in copiesobtained), reduced variations in the residual potential and thesensitivity even when used repeatedly a number of times, and excellentdurability.

This invention will now be illustrated in greater detail by reference tothe following examples. However, the invention is not intended to beconstrued as being limited to these examples. Unless otherwiseindicated, all parts are by weight.

EXAMPLE 1

A charge generating layer was formed by vacuum evaporation coating ofselenium in a layer of 0.4 μm thickness onto a grained aluminum platehaving a thickness of about 300 μm. Thereon, a solution prepared bydissolving 4 parts of the hydrazone compound (1) and 5 parts ofpolycarbonate of bisphenol A (trademarked Lexan-121, produced by GeneralElectric Co.) in 130 parts of dichloromethane was coated using a wirewound rod, and dried to result in formation of a charge transport layerhaving a thickness of about 5 μm. Thus, an electrophotographicphotoreceptor having a light sensitive layer constituting two layers wasobtained.

A negative potential of -5 kv was created on the surface of the thusobtained photoreceptor using a corona discharge device, that it, anelectrostatic copying paper testing apparatus (SP-428 model, produced byKawaguchi Electric Mfg. Co., Ltd.) and then, the surface was exposed tolight generated from a 3,000° K. of tungsten lamp under such conditionsthat the intensity of illumination at the surface was 10 lux. Theexposure was continued till the surface potential was reduced to halfthe initial potential, and from the time for such reduction, half decayexposure E₅₀ (lux·sec) was calculated.

The result was E₅₀ =9.5·lux sec.

The value of E₅₀ determined after the charging-exposure process wasrepeated 3,000 times was 9.9 lux·sex, and these results revealed thatvariation in sensitivity was very small.

EXAMPLES 2 TO 4

Photoreceptors No. 2, No. 3 and No. 4 were produced in the same manneras in Example 1 except that the hydrazone compounds (3), (9) and (10),respectively, were used in place of the charge transport substance usedin Example 1.

The E₅₀ value of each of these photoreceptors was determined in the samemanner as in Example 1. The results are shown in the following table.

    ______________________________________                                                        E.sub.50                                                      Photoreceptor   (lux · sec)                                          ______________________________________                                        No. 2           11.0                                                          No. 3            8.9                                                          No. 4           10.3                                                          ______________________________________                                    

EXAMPLE 5

A coating solution was prepared as follows: 5 parts of β-type copperphthalocyanine was added to 660 parts of dichloromethane and dispersedthereinto using supersonic waves. To the thus prepared dispersion wasadded 40 parts of polycarbonate of bisphenol A (Lexan-121, trademark)and 40 parts of the hydrazone compound (1), and they were dissolved inthe dispersion. The thus obtained coating solution was coated on aconductive transparent support (which had a vacuum evaporation coatingfilm of indium oxide on a polyethylene terephthalate film support havinga thickness of 100 μm, and exhibited a surface resistance of 10³ Ω)using a wire wound rod, and then dried. Thus, a light-sensitive layerhaving a thickness of about 10 μm was obtained.

After positive potential was created on this photoreceptor by +5 kv ofcorona discharge, sensitivity of this photoreceptor was determined inthe same manner as in Example 1. The value of E₅₀ in this case was 10.4lux·sec.

EXAMPLES 6 TO 12

Photoreceptors No. 6, No. 7, No. 8, No. 9, No. 10, No. 11 and No. 12were produced in the same manner as in Example 5 except that thehydrazone compounds (3), (4), (5), (6), (12), (18) and (19),respectively, were employed instead of the charge transport substanceused in Example 5.

The E₅₀ value of each of these photoreceptors was determined in the samemanner as in Example 5. The results obtained are shown in the followingtable.

    ______________________________________                                                        E.sub.50                                                      Photoreceptor   (lux · sec)                                          ______________________________________                                        No. 6           18.6                                                          No. 7           19.5                                                          No. 8            9.0                                                          No. 9           11.2                                                           No. 10         19.2                                                           No. 11         10.5                                                           No. 12          9.7                                                          ______________________________________                                    

EXAMPLE 13

Two parts of Chloro-Dian Blue (represented by the following structuralformula (c)) and the same parts of polycarbonate of bisphenol A(Lexan-121) were added to 260 parts of dichloromethane, and ground topowder and mixed with each other in a ball mill. Thus, a chargegenerating pigment dispersion was prepared. ##STR11##

The thus prepared dispersion was coated on a conductive transparentsupport (which had a vacuum evaporation coated film of indium oxide on apolyethylene terephthalate support having a thickness of 100 μm, andexhibited a surface resistance of 10³ Ω) using a wire wound rod, anddried the coat to result in the formation of a charge generating layerabout 1 μm thick.

Next, a solution dissolving 2 parts of the hydrazone compound (1) and 4parts of polycarbonate of bisphenol A (Lexan-121) in 60 parts ofdichloromethane was coated on the charge generating layer using a wirewound rod and then dried the coat to result in the formation of a chargetransport layer having a thickness of about 8 μm.

The value E₅₀ of the photoreceptor having the light-sensitive layerwhich the thus obtained two layers constituted was determined in thesame manner as in Example 1. The result was 5.0 lux·sec.

EXAMPLES 14 TO 16

Photoreceptors No. 14, No. 15 and No. 16 were produced in the samemanner as in Example 13 except that the hydrazone compounds (3), (5) and(18), respectively, were employed instead of the charge transportsubstance used in Example 13.

The E₅₀ value of each of these photoreceptors was determined in the samemanner as in Example 13. The results obbtained are set forth in thefollowing table.

    ______________________________________                                                        E.sub.50                                                      Photoreceptor   (lux · sec)                                          ______________________________________                                        No. 14          6.4                                                           No. 15          5.1                                                           No. 16          5.8                                                           ______________________________________                                    

EXAMPLE 17

A photoreceptor No. 17 was produced in the same manner as in Example 5except that the N-alkylamino substituted compound represented by thestructural formula (a) was employed for comparison instead of thehydrazone compound (1).

A positive potential was created by +5 kv of corona discharge on thesurface of the photoreceptor obtained in Example 5 and theabove-described photoreceptor No. 17, and thereafter each of the twophotoreceptors was examined in the decay of surface potential in thedark.

In FIG. 6, when the results are plotted, with surface potential asordinate and passage of time after charging as abscissa, dark decaycurves are obtained.

It is apparent from FIG. 6 that the dark decay characteristics aregreatly improved by the use of the N-arylamino substituted compoundinstead of the N-alkylamino substituted compound.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. An electrophotographic photoreceptor comprising aconductive support with a light-sensitive layer thereon containing ahydrazone compound represented by formula (I) or, (II): ##STR12##wherein X represents O, S or >N--R⁶ ; R¹ and R² each represents anon-substituted or a substituted straight or branched chain alkyl groupcontaining from 1 to 12 carbon atoms, a non-substituted or a substitutedstraight or branched chain aralkyl group containing from 7 to 20 carbonatoms, or a non-substituted or a substituted aryl group, the aryl groupincluding monovalent residues of monocyclic aromatic rings and condensedpolycyclic aromatic rings having from 2 to 4 rings therein; R³, R⁴ andR⁵ each represents hydrogen, a non-substituted or a substituted straightor branched chain alkyl group containing from 1 to 12 carbon atoms, anon-substituted or a substituted straight or branched chain aralkylgroup containing from 7 to 20 carbon atoms, a straight or a branchedchain alkoxy group containing from 1 to 4 carbon atoms, an aryloxy groupcontaining from 6 to 10 carbon atoms, an acyl group containing from 2 to8 carbon atoms, and alkoxycarbonyl group containing from 2 to 5 carbonatoms, a halogen atom, a nitro group, a monoalkylamino group whose alkylmoiety contains from 1 to 4 carbon atoms, a dialkylamino group whosealkyl moiety contains from 1 to 4 carbon atoms, or an amido groupcontaining from 2 to 8 carbon atoms; and R⁶ represents a non-substitutedor a substituted straight or branched chain alkyl group containing from1 to 12 carbon atoms, or a non-substituted or a substituted straight orbranched chain aralkyl group containing from 1 to 12 carbon atoms.
 2. Anelectrophotographic photoreceptor as in claim 1, wherein at least one ofthe groups represented by R¹ through R⁶ has a substituent group, and thesubstituent group is selected from a halogen atom, an alkoxy group, anaryloxy group, a dialkylamino group, and an alkylthio group.
 3. Anelectrophotographic photoreceptor as in claim 1, wherein at least one ofthe groups represented by R¹ through R⁶ is an aryl group which has asubstituent group, and the substituent group is selected from a halogenatom, an alkoxy group, an aryloxy group, a dialkylamino group, analkylthio group, and an alkyl group.
 4. An electrophotographicphotoreceptor as in claim 1, 2, or 3, wherein said light-sensitive layeris formed of (1) a charge transport medium comprising said hydrazonecompound and a binder, and (2) a charge generating substance dispersedin said charge transport medium.
 5. An electrophotographic photoreceptoras in claim 1, 2, or 3, wherein said light-sensitive layer is formed of(1) a charge transport layer containing said hydrazone compound and (2)a charge generating layer.
 6. An electrophotographic photoreceptor as inclaim 1, wherein the amount of said hydrazone compound in saidlight-sensitive layer ranges from 30% to 70% by weight, based on thetotal weight of said light-sensitive layer.
 7. An electrophotographicphotoreceptor as in claim 1, wherein said light-sensitive layer containsa sensitizing dye in an amount of from 0.1% to 5% by weight, based onthe total weight of said light-sensitive layer.
 8. Anelectrophotographic photoreceptor as in claim 4, wherein saidlight-sensitive layer contains 10 to 95 wt% of the hydrazone compoundand 50 wt% or less of the charge generating substance.
 9. Anelectrophotographic photoreceptor as in claim 5, wherein the amount ofsaid hydrazone compound in said charge transport layer ranges from 10wt% to 95 wt%, based on the total weight of said charge transport layer.10. An electrophotographic photoreceptor as in claim 1 wherein saidlight-sensitive layer comprises said hydrazone compound and a binder.